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Adding a timer to KeyListener

I extended a JFrame class and have my own model and JPanel extended classes as instance variables. I implemented KeyListener to my JFrame and it works with the arrow keys but my model moves extremely slow around the frame when I hold the keys down. My question is how do I attach the KeyListener methods to a timer or do something to make my model move faster when I hold the keys. Also if it is possible, how can the model move two directions at once, say left and up?
public class GameController extends JFrame implements KeyListener,ActionListener
{
private GamePieces p;
private GamePanel panel;
private Timer timer;
public GameController()
{
super("Balls");
setSize(800, 600);
timer = new Timer(10, this);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container c = getContentPane();
c.setLayout(new BorderLayout());
p = new GamePieces();
panel = new GamePanel();
p.addObserver(panel);
c.add(panel);
addKeyListener(this);
panel.update(p, null);
setResizable(false);
timer.start();
}
public void actionPerformed(ActionEvent e)
{
String actionCommand = e.getActionCommand();
if (e.getSource() == timer)
{
p.checkEat();
p.moveOthers();
panel.update(p, null);
}
}
public void keyTyped(KeyEvent e)
{
int s = 0;
}
public void keyPressed(KeyEvent e)
{
int key = e.getKeyCode();
if (key==38)
{
p.up();
panel.update(p, null);
}
else if (key==40)
{
p.down();
panel.update(p, null);
}
else if (key==39)
{
p.right();
panel.update(p, null);
}
else if (key==37)
{
p.left();
panel.update(p, null);
}
}
public void keyReleased(KeyEvent e)
{
int o = 0;
}
public static void main(String[]args)
{
GameController a = new GameController();
a.setVisible(true);
}
}

You are on right way but it should be a little more sophisticated. Follow MVC pattern. You should have model which remembers where you panel should be - up(), down() methods only update this model. You should have viewer which shows panel at current position. panel.update() belongs to viewer. And then you should have controller which changes position (invoke these up and down, left and right) and invokes viewer when necessary - to show movement or just next frame.
Your KeyListener tells controller to move position in some intervals when key is pressed. And then it tells controller to stop doing so when key is released. See, all parts move smoothly and independently. Keylistener tells controller what to do, controller does - changes model and invokes viewer. Model does nothing - only holds data. Viewer does nothing only shows current data.
P.S. Don't forget thread safety since you will press multiple keys and they will invoke controller multiple times in the same thread.

Clicking out of a Canvas

I am making a Pong program, and I have a start button that begins to draw everything, and quite literally to get the ball rolling (you're welcome for the pun). Anyways, when I hit the start button, a Key Listener to move the paddles won't work unless I click the mouse somewhere on the canvas to give it priority. Is there some sort of code to automatically "click" on the canvas without the user being hassled to do so? Thanks in advance.
This Is running awt by the way. I realize I should learn swing, but never got around to it.
public class Pong extends Applet implements ActionListener, KeyListener
{
Canvas c1;
Graphics myG;
Button start;
ball ball;
paddle LPaddle;
paddle RPaddle;
public void init()
{
this.setSize(1300,700);
c1 = new Canvas();
add(c1);
c1.addKeyListener(this);
c1.setBackground(Color.pink);
start = new Button("Start");
add(start);
start.addActionListener(this);
ball = new ball();
LPaddle = new paddle();
RPaddle = new paddle();
myG = c1.getGraphics();
}
public void paint(Graphics g)
{
c1.setLocation(0,0);
c1.setSize(1251,700);
start.setLocation(1255,350);
start.setSize(40,20);
}
public void keyPressed(KeyEvent e)
{
if(e.getKeyCode()==KeyEvent.VK_UP)//up
{
RPaddle.erasePaddle(myG);
RPaddle.movePaddleUp();
RPaddle.drawPaddle(myG);
}
if(e.getKeyCode()==KeyEvent.VK_DOWN)//down
{
RPaddle.erasePaddle(myG);
RPaddle.movePaddleDown();
RPaddle.drawPaddle(myG);
}
if(e.getKeyCode()==KeyEvent.VK_W)
{
LPaddle.erasePaddle(myG);
LPaddle.movePaddleUp();
LPaddle.drawPaddle(myG);
}
if(e.getKeyCode()==KeyEvent.VK_S)
{
LPaddle.erasePaddle(myG);
LPaddle.movePaddleDown();
LPaddle.drawPaddle(myG);
}
if(e.getKeyCode()==KeyEvent.VK_ENTER)
{
myG.drawLine(625,0,625,700);
LPaddle.setInitial(150,0,350);
RPaddle.setInitial(150,1250,350);
LPaddle.drawPaddle(myG);
RPaddle.drawPaddle(myG);
}
}
public void keyReleased(KeyEvent e)
{
}
public void keyTyped(KeyEvent e)
{
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==start)
{
myG.drawLine(625,0,625,700);
LPaddle.setInitial(150,0,350);
RPaddle.setInitial(150,1250,350);
LPaddle.drawPaddle(myG);
RPaddle.drawPaddle(myG);
}
}

KeyListeners are low level interfaces which have a major, significant draw back: The componet they are registered to must be focusable and be focused.
By clicking the start button, you are giving the button focus.
You could call requestFocusInWindow on the instance of the canvas, but this assumes that the the canvas is focusable in the first place.
If you can, you'd be better of using a JComponent/JPanel as the base for your game canvas and use the key bindings API.

JPanel redraw problem

I have JFrame, and I added my JPanel class with paintComponent() method. For example I drawed red rectangle, and after some action I want to draw green oval. I tried to call repaint() method in JPanel but nothing happens. Help me please!
UPDATE: It's just example code
public class Test extends JFrame implements ActionListener{
private Container content;
private MyPanel em;
private JButton btn;
Test() {
super("test");
content = getContentPane();
em = new MyPanel();
conent.add(em);
btn = new JButton("Draw");
btn.addActionListener(this);
content.add(btn);
}
public void actionPerformed(ActionEvent e) {
em.setShape("oval");
}
public class MyPanel extends JPanel {
private String shape = "rectangle";
MyPanel()
{
}
setShape(String shape){
this.shape = shape;
repaint();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
if(shape == "rectanle")
g.drawRectangle(100,25,100,200);
}
else if(shape == "oval"){
g.drawOval(100, 25, 175, 175);
}
}

Try calling markCompletelyDirty(myComponent) on javax.swing.RepaintManager.

Try replacing shape == "oval" with "oval".equals(shape). In Java, Strings that are equal according to equals() are not necessarily equal according to ==.
Also, I'd suggest you replace the string literals with constants:
class Whatever {
private final static String OVAL = "oval";
public void process(String arg) {
if (OVAL.equals(arg)) {
// Do something
}
}
}
to avoid problems with spelling mistakes (like you have with "rectangle" and "rectanle").
You could add debugging statements to check that the actionPerformed method is actually being called, and to see when paintComponent is executed and trace what path it takes through your code.
By the way, the code as posted shouldn't compile: you have mismatched braces.

repaint() not called when running app from Eclipse?

I never get "paint" written to my command line window when I use Eclipse and Run->cmd to run the program. It works fine if I run System.out.print() from paintComponent in another program. Someone who can help?
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class GUI extends JPanel implements KeyListener, ActionListener
{
private static final long serialVersionUID = 1L;
JFrame frmMain = new JFrame("Kodning");
JTextField text = new JTextField();
JPanel pan = new JPanel();
static char bokstav;
static int x=10, y=80;
boolean convert = false;
String s;
Timer t = new Timer(10, this);
public static void main(String[] args)
{
#SuppressWarnings("unused")
GUI g = new GUI();
}
public GUI()
{
frmMain.setSize(600, 120);
frmMain.setLayout(new GridLayout(2, 1));
frmMain.addWindowListener(hornStang());
frmMain.add(text);
frmMain.add(pan);
frmMain.setFocusable(true);
frmMain.setVisible(true);
frmMain.addKeyListener(this);
text.addKeyListener(this);
pan.addKeyListener(this);
t.start();
}
private static WindowAdapter hornStang()
{
return new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
};
}
public void keyPressed(KeyEvent e)
{
if(e.getKeyCode()== KeyEvent.VK_ENTER)
{
System.out.println("dechifrera");
repaint();
deshiffrera(text.getText());
}
}
public void keyReleased(KeyEvent arg0){}
public void keyTyped(KeyEvent arg0){}
public void deshiffrera(String s)
{
s = this.s;
repaint();
}
#override
public void paintComponent(Graphics g)
{
System.out.println("paint");
for(int i=0;i<s.length();i++)
{
bokstav = s.charAt(i);
switch (bokstav)
{
case 'a':nere(g); hoger(g); prick(g, 0); break;
//en massa case
default:break;
}
x=x+12;
}
}
#Override
public void actionPerformed(ActionEvent e)
{
repaint();
}
}

The component must be added to a visible window/frame/component for it's paintComponent to be called.
GUI is only added as a KeyListener but is neither added to the JFrame, nor any other visible component in the code above. There is no reason for calling paintComponent since the component is not being displayed at all.

There are a number of issues with your code:
Your GUI panel is not in the frame (shouldn't it be added instead of pan?)
String s is uninitialized, which causes a NullPointerException
paint should be overridden instead of paintComponents
paint should not change the state of the component, because it can be called any time.
etc...

You probably miss the output of "System.out.println("paint");" ?
GUI-Apps under Windows cant write to the console (they dont have a console, because it would suck if every GUI-App would also open a black window).
There are two java-interpreters under windows: "javaw.exe" which is a GUI-App and silently discards any System.out-writes. And "java.exe" which is a console-app and allows writing to the console. Try to start your program with "java.exe"

I use this with AWT (not 100% sure whether it's working in Swing too...)
Graphics g = _yourcomponent_.getGraphics();
if (g != null) {
_yourcomponent_.paint(g);
// below the estimated code for Swing:
_yourcomponent_.paintComponent(g);
}

How to "do something" on Swing component resizing?

I've a class which extends JPanel. I overwrote protected void paintComponent(Graphics g).
There is a variable which has to be recalculated when the panel's dimensions change. How do I do that in a proper way?

Like Adam Paynter suggested, you can also add an inner class to your code, like this:
class ResizeListener extends ComponentAdapter {
public void componentResized(ComponentEvent e) {
// Recalculate the variable you mentioned
}
}
The code you have entered between the innermost brackets will be executed everytime the component get resized.
Then you add this listener to your component with
myJPanel.addComponentListener(new ResizeListener());
You can get your component by using e.getComponent(). This way you can call any method of your component from inside the inner class like
e.getComponent().getWeight();

I suppose you could override the various setSize and resize methods and perform the calculation there. However, you may not find all the places where the size can be changed. You may want to have your class implement ComponentListener and simply listen to itself for resize events.
Warning: I am not a Swing expert.
Warning: I have not compiled this code.
public class MyJPanel extends JPanel implements ComponentListener {
public MyJPanel() {
this.addComponentListener(this);
}
public void paintComponent(Graphics g) {
// Paint, paint, paint...
}
public void componentResized(ComponentEvent e) {
// Perform calculation here
}
public void componentHidden(ComponentEvent e) {}
public void componentMoved(ComponentEvent e) {}
public void componentShown(ComponentEvent e) {}
}

If I understand the question correctly then you should read the section from the Swing tutorial on How to Write a Component Listener which shows you how to listen for a change in a components size.

If the calculation isn't time consuming, I would just re-calculate the value each time in paintComponent().
Otherwise, you can save a value that is the size of the component and check it against the new size in paintComponent. If the size changed, then recalculate, otherwise don't.
private Dimension size;
protected void paintComponent(Graphics g){
if (!size.equals(getSize())){
size = getSize();
// recalculate value
}
}
Or, you can do the calculation on a resize event.
//in the constructor add the line
addComponentListener(resizeListener);
private ComponentListener resizeListener = new ComponentAdapter(){
public void componentResized(ActionEvent e){
// recalculate value
}
};

The simplest way is to implement a ComponentListener:
myjpanel.addComponentListener(new ComponentAdapter() {
#Override
public void componentResized(ComponentEvent e) {
//recalculate variable
}
});
Here, I have used a ComponentAdapter because I only intend on overriding componentResized().

Here's what I use (where CoordinatePlane is a JPanel):
I'm not an expert
public CoordinatePlane() {
setBackground(Color.WHITE);
this.addComponentListener(new ComponentAdapter(){
public void componentResized(ComponentEvent e) {
//YOUR CODE HERE
}
});
}

It resizes automatically if it's
inside a BorderLayout panel and
put there as BorderLayout.CENTER component.
If it doesn't work, you probably have forgotten one of these two.

This simple example is drawing a red circle in the resized frame....
import java.awt.*;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import javax.swing.*;
import java.awt.geom.*;
public class RedCircle extends JFrame implements ComponentListener {
int getWidth;
int getHeight;
public RedCircle() {
super("Red Circle");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addComponentListener(this);
pack();
setVisible(true);
}
public void componentResized(ComponentEvent e) {
getWidth = e.getComponent().getWidth();
getHeight = e.getComponent().getHeight();
Panel pane = new Panel(getWidth,getHeight);
add(pane);
}
public static void main(String[] args) {
RedCircle rc = new RedCircle();
}
public void componentMoved(ComponentEvent e) {
}
public void componentShown(ComponentEvent e) {
}
public void componentHidden(ComponentEvent e) {
}
}
class Panel extends JPanel {
int panelWidth;
int panelHeight;
public Panel(Integer getWidth,Integer getHeight) {
panelWidth = getWidth;
panelHeight = getHeight;
}
public void paintComponent(Graphics comp) {
super.paintComponent(comp);
Graphics2D comp2D = (Graphics2D) comp;
int realWidth = panelWidth - 17;
int realHeight = panelHeight - 40;
float Height = (realHeight);
float Width = (realWidth);
// draw the Red Circle
comp2D.setColor(Color.red);
Ellipse2D.Float redCircle = new Ellipse2D.Float(0F, 0F, Width, Height);
comp2D.fill(redCircle);
}
}